The case was several times considered by the supreme court before the final judgment of affirmance was rendered, and the record contains four opinions, filed at different times in the course of the proceeding, from which it appears, in the most positive manner, that the decision of the cause in favor of the company was placed entirely on the ground of estoppel, as set up in the cross-bill. The original title of the county is nowhere, in any of the opinions, disputed or denied. A motion is made to dismiss the writ to this court for want of jurisdiction, on the ground that no federal question is involved. To give us jurisdiction of a writ of error for the review of the judgment of a state court, it must appear affirmatively, not only that a federal question was raised and presented for decision to the highest court of the state having jurisdiction, but that it was decided, or that its decision was necessary to the judgment that was rendered. The cases to this effect are numerous. Murdock v. Memphis, 20 Wall. 590, 636; Chouteau v. Gibson, 111 U.S. 200; S.C.. 4 SUP. CT. REP 340. This record shows that there were two questions presented by the pleadings, to-wit: (1) Whether the county acquired a title in equity to the lands in dispute under the operation of the swamp-land act, supplemented as it was by the act of March 3, 1857; and (2) whether, if it did, it was estopped by its subsequent acts from setting up that title as against the railroad company.

It may be conceded that the first of these questions was federal in its character, but we are clearly of opinion the second was not. A consideration of no act of congress was involved in its decision. There was nothing in the swamp-land grant to prevent the county from surrendering the property to the railroad company, if that was thought best. Under this defense the validity of the original title was not disputed. The claim was that, in legal effect, that title had been ceded to the railroad company, and that the county was in no condition to demand it back. There was no dispute about the federal right itself, but about the consequences of what had been done by the parties in respect to it, after the title had passed in equity from the United States to the county. To our minds, for the purposes of the present question, the case is, in all respects, the same as it would be if the dispute had been about the effect of an instrument intended as a conveyance of the property from the county to the company. The controversy is not as to the right to convey, but as to the effect of what has been done to make a conveyance. That depends, not on federal, but on state law.

It is contended, however, that inasmuch as the alleged compromise between the county and the company included, among other things, the claim of the county for taxes levied on the lands, the right to tax the lands before a patent was issued for them by the United States must have been passed upon by the court below in the decision which was rendered. Clearly this is not necessarily so. The company claims nothing under the taxation. Its rights against the county do not depend on the validity of the taxes. The right to tax was one of the matters in dispute between the county and the company, and that was compromised with the rest. The effect of the compromise upon the title of the county would be the same whether the tax was properly levied or not. It follows, therefore, that the decision of the court below on this branch of the case did not involve the question of the validity of the title set up by the county under laws of the United States. This brings us to the inquiry whether it appears sufficiently that the case was disposed of below on this defense. If it does, the motion to dismiss must be granted, and, having no jurisdiction, we cannot pass on the correctness of that decision.

The record discloses that this separate and distinct defense was made, and that it in no way depended on the validity or invalidity of the original title of the county. In our opinion it is clearly to be inferred from the decree of the court of original jurisdiction, which was affirmed in the supreme court, that the decision in favor of the company was placed entirely on that ground. So far as the original bill of the county is concerned, the decree finds in favor of the company, and dismisses the bill. Then, as to the cross-bill, it finds the legal title to be in the company, and that the county is estopped from claiming the lands, or denying the company's title thereto. This of itself implies that there was in fact no decision against any right, title, privilege, or immunity claimed under the constitution or laws of the United States, and that the decree rested alone on the defense of estoppel, which was broad enough to control the rights of the parties without disposing of the federal question which it was attempted to raise. In other words, it was adjudged by the state court that the title of the company must prevail in this suit because the county was precluded by its conduct from insisting to the contrary. But if we look to the opinions which, under the laws of Iowa, must be filed before a judgment is rendered, and which, when such is the law, may certainly be looked at to aid in construing doubtful expressions in a decree, it is shown, unmistakably, that the decision was put on that ground alone. Gross v. U.S. Mortgage Co.108 U.S. 486, 487; S.C.. 2 SUP. CT. REP. 940.

In the petition which was presented to the chief justice of the court for the allowance of a writ of error, it was stated 'that in the pleadings, record, and judgment and decree, there were drawn in question' the rights of the county under the swamp-land acts, as well as the construction of the land-grant acts, and that the judgment was against these rights. The chief justice, in his allowance of the writ, certified that he found the statements in the petition to be true; but, if this certificate is to have any effect at all upon this question, it certainly cannot be taken as conclusive when the same chief justice, in an opinion on file in the case, places the decision entirely on the ground of estoppel. It follows that we have no jurisdiction, and the motion to dismiss is granted.